1. Field of the Invention
The present invention relates to a brightness distribution display technology of an image pickup apparatus for displaying on the display screen the brightness distribution of an electronically retrieved subject image.
2. Description of the Related Art
A digital camera has conventionally been well known as one of the image pickup apparatuses for electrically retrieving a subject image (also referred to as a shot image), and recording the retrieved image as digital data on a storage medium such as Compact Flash (registered trademark), Smart Media (registered trademark), etc.
The digital camera electrically retrieves a subject image through an image pickup device such as a CCD (charge coupled device), etc., performs digitization on the retrieved image, and displays a digital image of the subject on the display screen (display unit) of, for example, liquid crystal, etc. configured in the body of the camera. These operations are constantly performed not only when a shutter button is pressed for shooting a subject image, but also when the shooting mode of the digital camera is in the standby state for shooting (the state in which the shutter button is ready for pressing). In the standby state for shooting, a thin image (through image) of a subject image sequentially retrieved from the image pickup device can be displayed on the display unit. The photographer can always view the subject image on the display unit although the digital camera is in the standby state for shooting.
When a subject is shot using the above-mentioned digital camera, it is necessary as in the case of shooting a subject using a conventional photographic film camera to set various conditions by determining the angle of view, performing focusing, determining the exposure condition by adjusting the iris and the shutter speed, etc.
The above-mentioned determination of the exposure condition in the condition settings can be performed by the digital camera normally using the metering unit performing metering of a specific range within the angle of view, and the iris and the shutter speed can be adjusted based on the metering result. The adjustment in the digital camera, for example, during shooting, is performed by computing the brightness value of a subject according to the shooting signal in the specific range retrieved from the CCD before shooting, and setting the value as a metering value by the metering unit. Based on the diagram of the program showing the relationship among the metering value, the shutter speed, etc., the conditions of the iris and the shutter speed for the metering value in the specific range metered by the metering unit are computed, and the adjustment of the iris and the shutter speed is automatically performed to satisfy the conditions. The specific range can be varied. The specific range can be narrowed to perform spot metering for metering on a point, the metering value computed from the brightness value in each range is held by metering a plurality of ranges within the angle of view, and multi-metering can be performed based on the average of the held metering values.
Thus, the digital camera is constantly adjusted to obtain correct exposure of a shot image when an image is shot.
However, correct exposure may not be obtained during shooting in an unexpected shooting environment, or it may be difficult to obtain correct exposure based on the likings of all photographers eventhough the shooting environment is acceptable.
Therefore, with the above-mentioned digital camera, it is common that a photographer can adjust the exposure condition by himself or herself.
To allow the photographer to adjust the exposure condition by himself or herself, the Patent Publication (Japanese Patent Application Laid-open No. 2001-245204) discloses the following technology.
In the disclosed technology, to appropriately adjust the exposure condition of the shot image displayed on the display screen, the Patent Publication discloses an example of computing the brightness value of each pixel of the shot image displayed on the display screen, obtaining a statistic (count value) of the number of pixels for each computed brightness value, and overlaying the brightness distribution chart obtained as the statistical result on the shot image on the display screen, and displaying the overlaid image, and an example of displaying a colored brightness distribution chart by coloring and displaying the brightness distribution chart depending on the brightness value, coloring the brightness distribution chart when the adjustment of the exposure condition by the photographer reaches the limit, etc. Using the brightness distribution chart, the balance of the brightness value can be recognized at a glance eventhough the entire shot image is too bright or too dark. Therefore, the photographer can appropriately adjust the exposure condition.
Normally, the latitude (also referred to as a dynamic range) of a shot image is narrower in the digital camera than in the conventional photographic film camera. Therefore, if a subject is shot under the exposure condition based on the metering result in a specific range, there occurs a white spot or blacking on a generated subject image depending on the shooting environment.
The digital camera normally defaults to the metering, centering on the center of the subject, and when the subject is shot, an exposure condition is set such that correct exposure can be applied to the shooting range (autoexposure capability). Therefore, for example, during shooting in back-lit conditions, only the center of the subject is dark and the surrounding portions are bright in the sunshine. As a result, if the metering is performed at the center of the above-mentioned subject, the brightness distribution chart shows a bias toward higher brightness values entirely, and the chart shows an overexposure state.
Thus, for a brightness distribution chart for the balanced brightness value of the entire subject image, the purpose of the autoexposure capability (AE for short) is not the value of the entire subject image, but the correct exposure of a predetermined area. Therefore, although the correct exposure can be obtained by the above-mentioned AE, it is natural that the impression from the brightness distribution chart is quite different.
The conventional technology has never indicated the relationship between the brightness distribution in a predetermined range of a subject image such as a range specified by the AE, etc. and the brightness distribution chart.
Furthermore, a digital camera can indicate a difference between a shot image actually shot by adjusting the exposure condition and a subject image displayed on the display unit before the shooting. The difference comes from the differences in various setting conditions between the standby state for shooting and the shooting. The practical differences in the setting conditions are those in the iris settings before and during shooting when a there is a flash working on the subject only when the subject is shot and when a moving subject is shot, or the exposure condition settings before and during shooting when there are different shooting environments before and after the shooting of a moving subject.
Therefore, there are a few objects to be deleted from shot images.
The digital camera has the function of reviewing a shot image on the display screen immediately after the shooting. With the function, the display time depends on the amount of data of the shot image, and a shot image of a small amount of data is displayed on the display screen only for a short time.
In the conventional technology, a digital camera has no function of checking the details of a shot image.